Laser implemented transmyocardial revascularization shows great promise for heart patients, but it does have some medical obstacles associated with it. The heart is extremely sensitive to laser pulses at certain times during its cycle. A laser pulse striking the heart at the T time of the ECG wave, for example, could cause the heart to fibrillate and result in heart failure. If the heart is stopped during the procedure this problem can be avoided. But stopping the heart requires cooling the heart and connecting the patient to a heart-lung machine with all the attendant increased risks that this brings including prolonged recovery times. A beating heart, on the other hand, is difficult to administer this technique to because as the heart contracts and expands the surface may not remain normal to the laser beam, the heart wall changes distance from the focus of the beam, and the thickness of the wall changes so that the positioning of the laser handpiece and the power of the beam required are varying and unpredictable. This makes precise location of laser beam on the heart difficult so that not only will the holes not be properly located, but other areas of the heart which should not be struck may well be struck.
Laser implemented transmyocardial revascularization also raises problems of a technical nature: lasers suitable for generating pulses of the necessary power and duration are quite expensive. One approach to creating such pulses in a continuous laser is to maintain a continuous electrical discharge in the laser but flow the gas through the discharge region at such a velocity that the gas is only in the discharge region for a short time. While each volume of gas responds as if pulsed, the effect is in fact a continuous laser with ten times the power of slow flow or of a sealed laser.
However, to obtain such high-speed gas flow a high-speed gas pump and a heat exchanger capable of cooling the gas are required. These are expensive, large, noisy, and consume substantial power. But this is a preferred approach in many medium and low-speed pulsed laser systems.
In some applications, pulses of longer duration are required which are too long to obtain the energy conversion without heating the gas and thus decreasing the population inversion ratio yet are not long enough to require continuous high speed gas flow. Thus it is inefficient and expensive to maintain the high-speed pump and heat exchanger continuously for these applications.